Medical devices used to monitor and/or provide therapy to a patient are often powered by an energy storage device, such as a battery. If the energy storage device becomes depleted, the medical device may no longer be able to perform these functions. In some cases, unexpected depletion of the energy storage device prior to or during use of the medical device to treat a patient may jeopardize the patient's life. For example, external defibrillators may be used to respond to medical emergencies, such as sudden cardiac arrest (SCA). If an energy storage device of an external defibrillator were depleted unexpectedly during treatment of a patient, the patient might not be resuscitated.
Consequently, some medical devices, such as external defibrillators, provide an indication of the status of an associated energy storage device, e.g., a battery charge status indication. For example, some existing medical devices provide an estimate of the percentage or fraction of the full energy storage capacity of the energy storage device that it currently stores. Other existing medical devices indicate an estimated amount of time remaining before the energy storage device is depleted.